Air separator with fluidized discharge



Sept. 27, 1966 F. RAsMUssEN 3,275,140

AIR SEPARATOR WITH FLUIDIZED DISCHARGE TTORNEY Sept. 27, 1966 F. RAsMUssEN 3,275,140

AIR sEPAHAToR WITH FLUIDIZED DISCHARGE Filed April ll, 1963 v 2 Sheets-Sheet 2 FIG. 3

INVENTOR.

ATTORNE Y;

3,275 140 AIR SEPARATOR WITH FLUIDIZED DISCHARGE Frits Rasmussen, Copenhagen-Valby, Denmark, assignor to F. L. Smidth & Co., New York, N.Y., a corporation of Delaware Filed Apr. 11, 1963, Ser. No. 272,288 Claims. (Cl. 209-139) This invention relates to air separators for separating nely divided material into coarse and line fractions and is concerned more particularly with an improved air separator of the closed circuit type which offers a number of advantages over similar separators as constructed heretofore.

In one well-known type of closed circuit air separator, the material to be separated is thrown outward centrifugally in a thin sheet from a rotating spreader plate into Athe path of an upward current of air. The coarse particles are not entrained in the air stream and fall into an inner collecting chamber, while the tine particles are carried lalong in the current and, subsequently, fall out of the stream in an outer collecting chamber, in which the velocity of the air current is reduced. The air current is then directed upward past the rotating plate and the separating action described continues.

In a conventional closed circuit air separator, the lower Vparts of the collecting chambers are conical and are provided with bottom openings, from which outlet pipes lead. As the outer chamber for collecting lthe tine fraction surrounds the inner chamber for collecting the coarse fraction, the outlet pipe for the coarse fraction necessarily eX- tends Iacross part of the outer chamber and passes outward throu-gh the wall of that chamber. In order that the material may flow to the bottom openings of the chambers, the chamber walls must be inclined at an angle greater than the angle of repose of the material collected, and the cross-sectional areas of the chambers must taper to the size -of the outlet pipes. Also, the oulet pipe from the inner chamber must pass through the outer chamber at .an inclination at least equal lto the angle of repose of one of their objectionable features.

When the coarse fraction leaving a separator is passed through a closed circuit -grinding installation and then returned `to the separator, as is often the case, the power consumed by the elevator or conveyor for returning the `material to the separator depends in part on the distance between the levels of the separator inlet andthe outlet for the. coarse fraction. It is, therefore, desirable to reduce this difference in ,level as much as is reasonably possible and thus lower the power consumption.

The. closed circuit air separator of the present invention is superior to similar priorseparators in that it is provided with means by which at least one of the fractions is uidized, so that the fraction may ow out of the separator in a fluidized state. As a result of Ithe uidization of the fraction, it is no longer necessary Ito provide the chamber containing the fraction with a conical or funnel-shaped 'bottom having walls inclined at an .angle greater than the angle of repose of the fraction and the height of the charnber may be substantially reduced. Preferably, the collecting chamber for the ne fraction is provided with the means for fluidizing the material and lthe bottom of this chamber is provided with a closure which extends annularly around the inner collecting chamber, in which the coarse fraction is collected. The closure may be airpervious and supplied with air from a chamber beneath it, although other known lluidizing means may be employed, it desired. The closure is symmetrical in relation United States Patent() ber of respects.

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to a vertical plane passing through the axes of the separator and the outlet for the tine fraction and slopes downward toward the outlet at such an angle as to .insure that the uidized material will ilow over the surface of the closure to the outlet.

Although the coarse fraction, if passed through a closed circuit grinding installation, may contain crushed grinding bodies and coarse lumps of material originating from the grinding mill, which make lluidization difcult, the chamber .for collecting the coarse fraction may be provided with means for uidizing the fraction', if desired. In that case, the bottom closure of the chamber is symmetrical in relation to a vertical plane passing through the axes of the separator and the outlet pipe for the coarse fraction and slopes downward toward the pipe. The closure may have air-pervious areas along its circumference and along a diameter leading to the outlet pipe and the -uidizing air maybe diffused through the air-pervious areas of the closure from an air chamber beneath the closure.

For a better understanding of the invention, reference may be made to the accompanying drawings, in which FIG. 1 is a view partly in elevation and partly in vertical `section of one form of separator embodying the invention;

FIG. 2 is a sectional view on the line 2-2 of FIG. 1;

FIG. 3 is a view similar to FIG. 1 of a modified form of the separator; and

FIGS. 4 and 5 are sectional views on the lines 4-4 and 5 5, respectively, of FIG. 3. v

The separator shown in FIGURE 1 is of the closed circuit type and of conventional construction in a num- It includes a casing 10 having .an inlet pipe 11 for feeding material to be separated into a hopper 12 leading to a spreader pl-ate 13 mounted on a vertical shaft 14 driven by a motor 15 mounted on top of the casing. A hollow hub 16 attached to the plate carriers a plurality of fan blades 17 near the top of the casing and the space within the casing below the blades is subdivided by a partition 18 into concentric chambers. The partition has a top opening and is provided ,at its lower end with ia series of adjustable vanes 19.

A conical collecting chamber 20 leads downward from the varies 19 and is provided with a detachable lower end section 21 having `an outlet'opening 22. An outer collecting chamber 23 attached to .fthe lower end off the casing 10 encircles the chamlber 20. The chamber 23 is annular in cross-section land has an outer conical wall 24 and an inner cylindrical w-all 25. The bottom 26 of -thechamber 23 is annular in shape and made of airpervious material, such as a porous plate. The bottom plate is inclined downwardly toward an outlet opening 27 at an angle steeper than the angle of repose of the iluidized ne fraction and is symmetrical in relation to a vertical plane through #the axes off the separator and of the opening 27. The bottom plate 26 forms the top of a chamber 28 which is supplied |with air under pressure through a suitable line.

In the operation of the separator described, the fan blades 17 maintain an upwardly owing current of lair from the vanes 19 through the chamber inside the partition 18 and out through the opening at the top of the partition. The stream then flows radially outwardly through the casing and down outside the partition 18 to the vanes. The material to be separated is lfed through the pipe 11 into the hopper 12 and falls upon the rotating spreader plate 13, lfrom which it is thrown into the path ofthe air stream. The heavier particles fall through the stream and collect as a coarse traction in the bottom end section 21 of the inner collecting chamber 20 to be removed through the opening 27. The fine particles are entrained in the air stream and are carried out through the opening 'at the top of the partition 18 and into the that the panticles drop out of the stream and collect in the outer chamber 23 upon the air-pervious bottom plate 26. The air flowing from the chamber 2S passes through the plate 26 and is diifused into the material to render it iiuent and the iluidized material then flows down the sloping bottom 26 to be discharged through the outlet opening 27.

In FIGURE l, the broken lines indicate the construction of the coarse and iine yfraction collecting chambers of a conventional closed circuit separator and it will be noted that the overall height of the separator of the invention is substantially less than that of the prior separator by reason of the outlet from the collecting chamber for the line material being .at a substantial height above the level where the outlet lies in the convention-al separator. Also, the distance between the level of the outlet romthe coarse collecting chamber and the level of the separator inlet is substantially reduced. By mak-Y ing the end section 21 of the inner collecting chamber 20 detachable, independent access to the tWoY chambers is provided and this facilitates repairs to theinterior of the separator.

The separator shown in FIGURE/3 is of the conventional closed circuit typeand includes a casing29 Within which are mounted a spreader plate and a fan driven by a motor 30.V The interiorof lthe casing is subdivided by -a partition similar to the partition 18 andthe material to be separated is fed through a pipe 31 into a hopper:

wall of the chamber at the` low point of the bottom plate l and through the wall of the chamber 32. The pipe 36 is f provided with yan air-pervious bottom plate 37,1which may be a continuation of the bottom plate 35,Y and the plates 35 and 37l form the top of a chamber 38 supplied with air through a suitable line. i The bottom 35 of'chamber 34 is symmetrical in relation -to a vertical plane through vthe axis of the separator and the outlet 39 at the outer end of the .passage 36. A pair of solid wedges 40 are mounted on top of the bottom plate 35, so that the airpervious` area of the bottom is formed of outer curved sections along the circumference of the plate and an area extending along the diameter of the plate and leading to the outlet pipe 36.

The separator shown in EIGURE 3 operates in the same `manner as that shown in FIGURE 1, except that the coarse traction collected in the chamber 34 is uidized and ows outward through the pipe 36, lwhile the line fraction is collected in the usual way in 4the outer collecting chamber 32 for discharge through the outlet 33.

In FIGURE 3, the shape of the collecting chamber for the coarse inaction and of the outlet pipe yleading from the chamber in a conventional separator are indicated in broken lines and it will be apparent that the differencek in level between the outlet from the collecting `chamber for the coarse fraction and the separator inlet in the new separator is substantially less than the corresponding distance in a conventional separator. As a result, when the separator of FIGURE 3 is used in closed circuit grind-4 separating a finely dividedmaterial in'to coarse and lineV fractions including .a substantiallyrclosed casing, means in said casing dening concentric inner and outer chamV bers spaced from the top of said casing,:Y said inner chamt ber :for `collecting the coarse. fraction and said outer chamber for collecting the iine traction, means for main` Y tainingfan air current flowing upwardly in the inner` chamber and .owing downwardly in the outer chamber, means for introducing finely divided material into the inner chamber 4for entrainrnentof the line fractionsin the air stream for transfer to Ythe outer chamber and collec-` tion of the coarse fractions in the inner chamber, an

inner chamber outlet insaid casing and outer chantber` outlet in said casing, the improvement in combination therewith comprising means for maintaining the 4distance k between the top of the casing `and the` chamber outlets at Ya minimum, said'means comprising an air pervious closure means for the bottom ofoneofthe chambers inclined toward said one chamber outlet for diiusing air z into thematerial above the closure to -uidize the material andv cause itto flow over the closure to the outlet.

, 2Q An air separator `as in claim 1 wherein the closure 1 closes the inner chamber and has` a perforated extension connected YIto an kinner chamber outlet positioned externally of saidcasing.y

3. An air separator as in claim 2 wherein .the closure Y is ,symmetrical in Vrela-tion to a vertical plane Apassing through the axis of the;v separator and the Iupper end of the inner chamber outlet. Y

4. An air separator as in claim `1 wherein the closureV closes fthe bottom of the outer chamber Yand is annular with the outer chamberoutlet positioned externally with` the casing at the low end of the annular closure.

5. An air separator as in claim 4 wherein the closure is symmetrical in relation to a vertical plane passing rthrou-gh the axis of the separator and the upper end of the outer chamber outlet.

References Cited by the Examiner ,FRANK w. LUTIER, Primary Examiner.

VKerr 302-29 X l 

1. IN AN AIR SEPARATOR OF THE CLOSED CIRCUIT TYPE FOR SEPARATING A FINELY DIVIDED MATERIAL INTO COARSE AND FINE FRACTIONS INCLUDING A SUBSTANTIALLY CLOSED CASING, MEANS IN SAID CASING DEFINING CONCENTRIC INNER AND OUTER CHAMBERS SPACED FROM THE TOP OF SAID CASING, SAID INNER CHAMBER FOR COLLECTING THE COARSE FRACTION AND SAID OUTER CHAMBER FOR COLLECTING THE FINE FRACTION, MEANS FOR MAINTAINING AN AIR CURRENT FLOWING UPWARDLY IN THE INNER CHAMBER AND FLOWING DOWNWARDLY IN THE OUTER CHAMBER MEANS FOR INTRODUCING FINELY DIVIDED MATERIAL INTO THE INNER CHAMBER FOR ENTRAINMENT OF THE FINE FRACTIONS IN THE AIR STREAM FOR TRANSFER TO THE OUTER CHAMBER AND COLLECTION OF THE COARSE FRACTION IN THE UPPER CHAMBER, AN INNER CHAMBER OUTLET IN SAID CASING AND OUTER CHAMBER OUTLET IN SAID CASING, THE IMPROVEMENT IN COMBINATION THEREWITH COMPRISING MEANS FOR MAINTAINING THE DISTANCE BETWEEN THE TOP OF THE CASING AND THE CHAMBER OUTLETS 